1. Field of the Invention
The present invention relates to to a process cartridge used preferably for an electrophotography method, an electrostatic recording method and an electrostatic printing method, an image forming apparatus and an image forming process.
2. Description of the Related Art
Recently, the image forming technique in a copier, a primter and a facsimilie machine has been remarkably developed. Among them, a technique which is most frequently used is a technique belonging to an electrostatic image forming process represented by the electrophotography method. The reason therefore is considered to be such advantages, that according to the imge forming process represented by the electrophotography method, an image having a high quality can be obtained in a high speed and an image not only in monochrome but also in color can be obtained, and that the imge forming process has a durability for a long period and a stability.
The electrophotography method is an image forming process by charging entirely the surface of an electrostatic latent image carrier (hereinafter, sometimes referred to as “photoconductive body”, “photoconductive body for the electrophotography” or “photoconductive insulating material”), by imparting to the electrostatic latent image carrier a light-exposure corresponding to an image which is to be formed, thereby forming an electrostatic latent image and by visualizing the electrostatic latent image with a toner.
As the photoconductive body for the electrophotography, an organic photoconductive body comprising an organic photo conductive substance is most widely used. The organic photoconductive body is more advantageous than another photoconductive body in that the organic photoconductive body can be easily developed as a material corresponding to various light sources for the light-exposure, such as from a visual light to an infrared light and can be produced with a low cost, and for the organic photoconductive body, a material causing no environmental pollution can be selected. On the contrary, the organic photoconductive body has such disadvantages that the organic photoconductive body has a low mechanical strength and that during the copying and printing in an amount of many sheets of the organic photoconductive body, a deterioration or a scratch is caused on the surface of the organic photoconductive body.
The organic photoconductive body is generally produced according to a method comprising disposing a charge generating layer on a conductive support comprising aluminum or an aluminum alloy by metallizing an organic charge generating substance over the support or by coating the support with a coating liquid in which an organic charge generating substance and an organic polymer compound which is used as an integrating agent are dispersed in a solvent and by disposing a charge transporting layer by coating the charge generating layer with a coating liquid in which an organic charge generating substance and an organic polymer compound which is used as an integrating agent.
Generally, in an electrophotography apparatus according to the Carlson method, after the photoconductive body is uniformly charged, an electrostatic latent image is formed by discharging the charged photoconductive body in the form of an image (i.e., a discharged portion of the photoconductive body forms the form of an image) by a light-exposure and the electrostatic latent image is developed and visualized with a toner, thereby fixing the resultant toner image through transferring the toner image to a paper or the like.
In this case, all toner on the photoconductive body are not transferred and a portion of the toner remains on the photoconductive body. When, while the toner remains, a new image-froming is performed, due to the remaining toner, the copying of an image having a high quality and no contamination cannot be obtained. Thus, a cleaning unit configured to remove the remaining toner becomes necessary. Representative examples of the cleaning unit include a fur brush, a magnetic brush and a blade. Among them, from the viewpoint of the performance and the composition of the apparatus, the blade is preferred. As the blade, an elastomeric gum rubber in the form of a plate is generally used.
Since thus, the surface of the photoconductive body for the electrophotography is directly subjected to an electrorical or mechanical external force by a condesator, a developing apparatus, a tranfering unit or a cleaning unit, the photoconductive body for the electrophotography is required to have durability against the external force, particularly mechanical durability against the causing of a wear or a scratch on the surface of the photoconductive body by the rubbing and against the film peeling of the photoconductive body by the invading of a foreign substance or by the shock during the coping with the paper clogging. Among them, the durability of the photoconductive body against the scratch and the film peeling by the shock is required to be improved to be higher.
For satiafying the above-noted required various properties, heretofore various trials have been studied. For example, with respect to the mechanicl durability, it is reported that by laminating on the surface of an organic photoconductive body a BPZ polycarbonate as a binder resin, the wearing properties and the toner filming properties of the surface of the photoconductive body can be improved. However, the above-noted photoconductive body comprising a BPZ polycarbonate laminated on the surface of the photoconductive body has yet unsatisfactory wearing properties and an unsatisfactory durability.
Further, it is reported that as the surface protective layer of the photoconductive body, a curable silicone resin containing a colloidal silica is laminated on the surface of the photoconductive body (see Japanese PatentApplication Laid-Open (JP-A) No. 06-118681). By the surface protective layer comprising a curable silicone resin containing a colloidal silica, the wearing properties of the photoconductive body can be improved. However, the electrophotographe property of the photoconductive body during the repeating use is yet unsatisfactory and a disadvantage is caused wherein not only the fog and the image blur are easily caused, but also the durability of the photoconductive body is unsatisfactory.
For improving these disadvantages, a photoconductive body comprising as the surface layer, a resin layer produced by bonding an electron-hole transportable compound modified by an organic silicone to a curable organic silicone polymer is proposed (see JP-A Nos. 09-124943 and JP-A 09-190004). In this proposal, since the surface layer is cured, the surface of the sensitive material is not abraded; however, the water adsorbed to the sensitive material in a high-temperature and high humidity atmosphere cannot be removed, so that an image blur and a filming of a paper powder or the toner are easily caused and a disadvantage is caused wherein an image failure in the form of a stripe or a dot is easily caused.
On the other hand, since not only the lessening of the diameter of the sensitive material is progressed by the downsize of the image forming apparatus, but also the movements of the speedup of the apparatus and of the maintainance-free are followed, it is desired that the photoconductive body has a further higher durability. From such a viewpoint, the organic photoconductive body has originally poor chemical stability and because the organic photoconductive body comprises mainly a charge transporting substance having a low molecuilar weight and an inactive polymer, the organic photoconductive body is generally soft, so that the organic photoconductive body has such a disadvantage that when the organic photoconductive body is repeatedly used in the electrophotography process, a wear due to a mechanical load applied by the developing system or the cleaning system is easily caused in the organic photoconductive body. Further, it is required that for improving the cleaning properties of the image forming apparatus according to the lessening of the diameter of tone particles for enhancing the image quality, the gum hardness and touching pressure of the cleaning blade are enlarged and such a requirement is a cause for accelerating the wear of the photoconductive body. The wear of the photoconductive body impaires the sensitivity and electrical properties (such as the charging properties) of the photoconductive body and becomes the cause for an anomalous image, such as the lowering of the image density and a dirty background. A scratch caused by a localized wear causes an image having a dirt in the form of a stripe due to an unsatisfactory cleaning and it is considered that in the present condition, the exhaustion of the life of the photoconductive body is rate-determined by the above-noted wear and scratch and the photoconductive body is led to the replacement.
Thus, for enhancing the durability of the photoconductive layer, it is indispensable to lower the wear degree of the photoconductive body and the lowering of the wear degree of the photoconductive body is most urgent problem to be solved in the present technical field.
Examples of the method for improving the hardwearing properties of the photoconductive layer include (1) a method in which a cross-linked charge transportable layer comprises a curing binder (see JP-A No. 56-48637), (2) a method in which a cross-linked charge transportable layer comprises a charge transportable polymer (see JP-A No. 64-1728) and (3) a method in which in the cross-linked charge transportable layer, an inorganic filler is dispersed (see JP-A No. 04-281461).
Among these methods, the method (1) using a curable binder has such a tendency that the compatibility of the curable binder with a charge transportable substance is poor and due to an impurity, such as a polymerization initiator and an unreacted residue, the residual electric potential of the charge transportable layer is elevated, so that the lowering of the image density is easily caused. In the method (2) using a charge transportable polymer, while the hardwearing properties of the photoconductive body can be improved to some extent, a photoconductive body which can fully satisfy the durability required for the organic photoconductive body is not yet obtained. Since the polymerization and purification of the materials for producing the charge transportable polymer is difficult and a charge transportable polymer having a high purity can be difficultly obtained, the electrical properties between the charge transportable polymer and another material can be difficultly stabilized. Further, a disadvantage in the production of the charge transportable polymer is sometimes caused wherein the viscosity of a coating liquid for producing the charge transportable layer becomes high. In the method (3) using an inorganic filler, the organic photoconductive body comprising a charge transportable layer in which an inorganic filler is dispersed can exhibit higher hardwearing properties than that of a photoconductive body produced by dispersing an usual charge transportable substance having a low molecular weight in an inactive polymer; however, the organic photoconductive body comprising an inorganic filler has such a tendency that due to a charge trap which is present on the surface of the inorganic filler, the residual electric potential of the charge transportable layer is elevated, so that the image density is easily lowered. Further, when the inorganic filler on the surface of the photoconductive body and the binder resin have a large unevenness, a cleaning-fault is caused and the cleaning-fault causes also the toner filming and the image delection sometimes.
Therefore, according to the methods (1), (2) and (3) heretofore, the general durability comprising the electrical durability and mechanical durability which is required for the organic photoconductive body is not yet fully satisfied.
For improving the hardwearing properties and scratch resistance of the photoconductive layer comprising a curing binder in the method (1), a photoconductive body comprising a multi-functional acrylate monomer cured form is proposed (see Japanese Patent (JP-B) No. 3262488). However, in this proposal, with respect to the above-noted photoconductive body, while it is described that a protective layer disposed on a photoconductive layer may comprise a charge transportable substance and comprises a multi-functional acrylate monomer cured form, there is no description explaining a specific improving method of the hardwearing properties and scratch resistance of the photoconductive layer. When the cross-linked charge transportable layer comprises a charge transportable substance having a low molecular weight, the compatibility of the charge transportable substance having a low molecular weight with the multi-functional acrylate monomer cured form is poor, so that in the photoconductive layer, the diposition of the charge transportable substance having a low molecular weight and the cloudiness are caused and a disadvantage is caused wherein not only the image density is lowered due to the elevation of the potential in a light-exposed portion, but also the mechanical strength of the charge transportable layer is lowered.
Moreover, since in the production of the above-noted photoconductive body, the material for the cross-linked charge transportable layer is reacted in the state of comprising a polymer binder with the monomer, the forming of a tree-dimensional network is not satisfactorily progressed and the cross linkage density becomes dilute, so that a rapid improvement of the hardwearing properties of the photoconductive body cannot have been yet obtained.
As a substitutional method of the above-noted methods for improving the hardwearing properties of the photoconductive layer, a method for disposing the charge transportable layer using a coating liquid comprising a monomer having a double bond of C═C, a charge transportable substance having a double bond of C═C and a binder resin is proposed (see JP-B No. 3194392). The binder resin has the function of improving the adhesion between the charge generating layer and the curable charge transportable layer and the function of relaxing the internal stress of the curable charge transportable layer during the curing thereof and is generally classified into two types, such as (1) a binder resin having a reactivity with the charge transportable substance through the C═C double bond and (2) a binder resin having no C═C double bond and no reactivity with the charge transportable substance.
The photoconductive body comprising the above-noted binder resin has the compatibility between the hardwearing properties and advantageous electrical properties thereof and attracts the attention; however, when a binder resin having no reactivity is used, the compatibility between the binder resin and the cured form produced according to the reaction between the monomer having a C═C bond and the charge transportable substance is poor and in the cross-linked charge transportable layer, a layer separation is caused, so that a scratch and an adhesion of an external additive in the toner or a paper powder are caused sometimes. Further, as noted above, the forming of a tree-dimensional network is not satisfactorily progressed and the cross linkage density becomes dilute, so that a rapid improvement of the hardwearing properties of the photoconductive body cannot have been yet obtained. Moreover, since the monomer described specifically in the above-noted patent document as a monomer having a C═C bond which is used for producing the photoconductive body is a bifunctional monomer, the photoconductive body comprisimg such a monomer has not yet satisfactory hardwearing properties. Even in the case where a reactive binder was used, while the molecular weight of the cured form was enlarged, the number of the intermolecular cross-linkage was small and the compatibility between the bond amount and cross-linkage density in the charge transportable substance was difficulty, so that the electrical properties and hardwearing proiperties of the photoconductive body were not satisfactory.
Further, a photoconductive layer comprising a cured form of an electron-hole transportable compound having plural chain polymerizable functional groups in one molecule is proposed (see JP-A No. 2000-66425). The photoconductive layer in which the cross-linkage density was enhanced had a high hardness; however, since a bulky electron-hole transportable compound had plural chain polymerizable functional groups, in the cured form, a strane was caused or an internal stress was enlarged, so that a disadvantage was caused wherein in the cross-linked surface layer, a cracking or a peeling is easily caused in the long-term using.
Accordingly, a photoconductive body comprising a cross-linked photoconductive layer to which a charge transportable structure is chemically bonded according to a conventional method, has not yet satisfactorily satisfiable general properties under the present condition and a further improvement and development have been desired.